1. Field of the Invention
Aspects of the present invention relate to a paper feeding apparatus of an image forming apparatus, and more particularly, to a paper feeding apparatus for reducing noise generated during paper feeding, and an image forming apparatus having the same.
2. Related Art
Noise generated by office machines used in offices or homes can result in reduced operating effectiveness. Noise is often generated when paper is picked up and fed into an image forming apparatus, such as a printer, a photocopier, a facsimile machine, or a multifunctional product. The noise may come from various sources, such as friction between mechanical components and the printable media or the steep slope of the transfer path. Accordingly, noise reduction apparatuses are increasingly required to maximize efficiency in noise-free environments.
FIG. 1 is a perspective view illustrating the structure of a general paper feeding apparatus employed in an image forming apparatus. As shown in FIG. 1, the general paper feeding apparatus used in the image forming apparatus comprises a pickup roller 15 and a pickup cam 19. A locking protrusion 13 is formed on one side of a pickup gear 11 and a clutch gear 12. A locking pawl 14 of a solenoid is locked by the locking protrusion 13. When a pickup signal is applied to the solenoid, the locking pawl 14 of the solenoid moves away from the locking protrusion 13, the clutch gear 12 is released, and the pickup gear 11 rotates. When the pickup gear 11 rotates, the pickup roller 15 picks up the uppermost sheet of printable media, such as paper, loaded in a paper cassette (not shown).
The printable medium picked up by the pickup roller 15 travels along a guide surface of a transfer guide 17, which has a predetermined curvature. An alignment roller 18 is mounted on an exterior of the transfer guide 17 to correct any paper skew occurring during the transferring process. Accordingly, the printable media are transferred to an image forming unit.
After the uppermost printable medium is picked up during one rotation of the pickup roller 15, the locking protrusion 13 of the clutch gear 12 is locked by the locking pawl 14 again, and the pickup gear 11 and the pickup roller 15 remain in a standby state until other pickup signals are received. The pickup cam 19 allows the pickup roller 15 to have a constant angle after rotating.
A paper feeding apparatus having the above structure is commonly employed and has been used for a long period of time. Currently, most printing machine manufacturers use the above paper feeding apparatus as a basic pickup and transfer device. However, the general paper feeding apparatus of the image forming apparatus has problems with noise generation.
FIG. 2 is a graph illustrating an example volume of noise as a function of time generated by the general paper feeding apparatus shown, for example, in FIG. 1. Firstly, in addition to operational noise 20a, noise 20b (generated by turning the solenoid on and off during the paper feeding) and noises 20c and 20d (generated when the pickup cam rotates and recovers) are also extremely unpleasant to the user. Secondly, while the pickup roller is in contact with the uppermost printable medium, friction occurs between the uppermost printable medium and a printable medium directly below the uppermost printable medium, generating dragging noise 20e. In particular, the rear portion of the uppermost printable medium is dragged along the printable medium directly below the uppermost printable medium as the uppermost printable medium passes through the transfer roller, generating friction and making noise.
Thirdly, friction noise is also generated when the printable medium travels over the guide surface of the transfer guide. In particular, the rear portion of the printable medium is rolled into a cylindrical shape by the transfer guide as the printable medium is being released from the guide surface. The rolled printable medium passes through an alignment roller and is thereby pushed into a substantially horizontal path. As a result, the printable medium rapidly unrolls, generating a shock noise 20f. 
Some printing apparatuses, as described in, for example, Japanese Patent Laid-open No. 05-139548, use a structure wherein a printable medium is picked up with a non-contact technique using electrostatic force, instead of using a roller. Although these printing apparatuses prevent the noise 20b due to the solenoid, the noises 20c and 20d remain, because the pickup roller lifts up only the front portion of the uppermost printable medium. The rear portion of the uppermost printable medium is still dragged along the printable medium directly below the uppermost printable medium during the transferring process.